RE: [PATCH] pdump: fix build issue with GCC 12

[Joyce Kong <Joyce.Kong@arm.com>]

> -----Original Message-----
> From: Tyler Retzlaff <roretzla@linux.microsoft.com>
> Sent: Monday, March 27, 2023 10:35 PM
> To: Joyce Kong <Joyce.Kong@arm.com>
> Cc: reshma.pattan@intel.com; stephen@networkplumber.org;
> konstantin.v.ananyev@yandex.ru; dev@dpdk.org; nd <nd@arm.com>;
> stable@dpdk.org; Ruifeng Wang <Ruifeng.Wang@arm.com>
> Subject: Re: [PATCH] pdump: fix build issue with GCC 12
> 
> On Mon, Mar 27, 2023 at 07:07:12AM +0000, Joyce Kong wrote:
> > The following warning is observed with GCC12 compilation with release
> > 20.11:
> >
> > In function ‘__rte_ring_enqueue_elems_64’,
> >     inlined from ‘__rte_ring_enqueue_elems’ at
> >             ../lib/librte_ring/rte_ring_elem.h:225:3,
> >     inlined from ‘__rte_ring_do_enqueue_elem’ at
> >             ../lib/librte_ring/rte_ring_elem.h:424:2,
> >     inlined from ‘rte_ring_mp_enqueue_burst_elem’ at
> >             ../lib/librte_ring/rte_ring_elem.h:884:9,
> >     inlined from ‘rte_ring_enqueue_burst_elem’ at
> >             ../lib/librte_ring/rte_ring_elem.h:946:10,
> >     inlined from ‘rte_ring_enqueue_burst’ at
> >             ../lib/librte_ring/rte_ring.h:721:9,
> >     inlined from ‘pdump_copy’ at
> >             ../lib/librte_pdump/rte_pdump.c:94:13:
> > ../lib/librte_ring/rte_ring_elem.h:162:40: warning: ‘*dup_bufs.36_42
> > + _89’ may be used uninitialized [-Wmaybe-uninitialized]
> >   162 |                         ring[idx] = obj[i];
> >       |                                     ~~~^~~
> > ../lib/librte_ring/rte_ring_elem.h:163:44: warning: ‘*dup_bufs.36_42
> > + _98’ may be used uninitialized [-Wmaybe-uninitialized]
> >   163 |                         ring[idx + 1] = obj[i + 1];
> >       |                                         ~~~^~~~~~~
> > ../lib/librte_ring/rte_ring_elem.h:164:44: warning: ‘*dup_bufs.36_42
> > + _107’ may be used uninitialized [-Wmaybe-uninitialized]
> >   164 |                         ring[idx + 2] = obj[i + 2];
> >       |                                         ~~~^~~~~~~
> > ../lib/librte_ring/rte_ring_elem.h:165:44: warning: ‘*dup_bufs.36_42
> > + _116’ may be used uninitialized [-Wmaybe-uninitialized]
> >   165 |                         ring[idx + 3] = obj[i + 3];
> >       |                                         ~~~^~~~~~~
> > ../lib/librte_ring/rte_ring_elem.h:169:42: warning: ‘*dup_bufs.36_42
> > + _129’ may be used uninitialized [-Wmaybe-uninitialized]
> >   169 |                         ring[idx++] = obj[i++]; /* fallthrough */
> >       |                                       ~~~^~~~~
> > ../lib/librte_ring/rte_ring_elem.h:171:42: warning: ‘*dup_bufs.36_42
> > + _139’ may be used uninitialized [-Wmaybe-uninitialized]
> >   171 |                         ring[idx++] = obj[i++]; /* fallthrough */
> >       |                                       ~~~^~~~~
> > ../lib/librte_ring/rte_ring_elem.h:173:42: warning: ‘*dup_bufs.36_42
> > + _149’ may be used uninitialized [-Wmaybe-uninitialized]
> >   173 |                         ring[idx++] = obj[i++];
> >
> > Actually, this is an alias warning as -O3 enables strict alias.
> > This patch fixes it by replacing 'dup_bufs' with '&dup_bufs[0]'
> > as the compiler represents them differently.
> >
> > Fixes: 278f945402c5 ("pdump: add new library for packet capture")
> > Cc: stable@dpdk.org
> >
> > Signed-off-by: Joyce Kong <joyce.kong@arm.com>
> > Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
> > ---
> 
> Acked-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
> 
> >  lib/pdump/rte_pdump.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/lib/pdump/rte_pdump.c b/lib/pdump/rte_pdump.c index
> > 9bc4bab4f2..53cca1034d 100644
> > --- a/lib/pdump/rte_pdump.c
> > +++ b/lib/pdump/rte_pdump.c
> > @@ -134,7 +134,7 @@ pdump_copy(uint16_t port_id, uint16_t queue,
> >
> >  	__atomic_fetch_add(&stats->accepted, d_pkts, __ATOMIC_RELAXED);
> >
> > -	ring_enq = rte_ring_enqueue_burst(ring, (void *)dup_bufs, d_pkts,
> NULL);
> > +	ring_enq = rte_ring_enqueue_burst(ring, (void *)&dup_bufs[0],
> > +d_pkts, NULL);
> 
> nit: i would drop the cast to void *, it shouldn't be needed?

Removing 'void *' here would generate a warning from incompatible pointer type, 
as rte_ring_enqueue_burst(struct rte_ring *r, void * const *obj_table, ...) expected 
'void * const *', but argument of &dup_bufs[0] is of type 'struct rte_mbuf **'.